Bleach system

ABSTRACT

1. IN AN ELECTROLYTIC PROCESS FOR REGENERATING A SPENT PHOTOGRAPHIC BLEACH SOLUTION CONTAINING FERROCYANIDE TO BE CONVERTED TO FERRICYANIDE, THE IMPROVEMENT WHICH COMPRISES ESTABLISHING AN ANNULAR ZONE BETWEEN AN INNER POSITIVELY CHARGED ELECTRODE AND AN OUTER NEGATIVELY CHARGED ELECTRODE POSITIONED WITHIN A RESERVOIR OF SPENT BLEACH SOLUTION, INTRODUCING SUFFICIENT AIR UPWARDLY THROUGH SAID ANNULAR ZONE SO AS TO CREATE A CIRCULATION OF SPENT SOLUTION UNDERGOING REGENERATION BETWEEN THE ELECTRODES AND TO DILUTE EVOLVED HYDROGEN SO AS TO SAFEGUARD AGAINST EXPLOSION.

E. YPALMONKA Nov. 5, 1974 BLEACH SYSTEM Filed Oct. 27, 1972 UnitedStates Patent 3,846,132 BLEACH SYSTEM Edward Palmonka, Elmont, N.Y.,assignor to EBR Development Corp., New York, N.Y. Filed Oct. 27, 1972,Ser. No. 301,281 Int. Cl. B01k 1/00; G03c 5/32 US. Cl. 96-60 R 5 ClaimsABSTRACT OF THE DISCLOSURE The present invention relates to theregeneration of spent photographic bleach solutions by use of concentricelectrodes with solution being circulated between the electrodes by theaction of air.

BACKGROUND In the processing of color photographic films, it is commonpractice to bleach out the silver image to silver bromide by a solutionof an alkali bromide and alkali ferricyanide so that after processing iscompleted, only the dye image remains. The silver bromide is thenremoved in the fixing bath and washing steps which follow, leaving thedye image.

In this process the ferricyanide is converted to ferrocyanide.

Similarly, bleach solutions are also used in black and white reversalprocesses where their function is to remove the negative silver image sothat upon completion of the processing, only the positive silver imageremains.

Various means have been suggested for regenerating spent ferricyanidetype bleach solutions used in photographic processing. Chemicalregeneration techniques, such as the use of water soluble persulfateshave been suggested. Such chemical oxidation techniques, however, oiferthe disadvantage of having to be done outside of the normal processingequipment, usually in a mixing tank after the processing tanks.Additionally, there is a danger of residual chemical oxidation which canseriously affect the color film processed.

As a means of further improving regeneration of bleach solutions,electrolytic means for oxidation of ferrocyanide back to ferricyanidehave been suggested. Such systems have in general previously not beenwidely adopted due to relatively high capital investment and maintenancecosts. Typical of such systems is the use of a porcelain or asbestosdiaphragm between two electrodes with pumps for circulating the solutionbetween the electrodes.

The present apparatus and process offers an extremely simple, adaptable,and low cost means for electrolytic regeneration of spent ferricyanidephotographic bleach solution. More particularly, two general cylindricalelectrodes are placed in a tank containing spent solution so as to havea substantial vertical orientation, i.e., either simply vertically, orat an angle inclined upwardly. The electrodes are concentric placed onewithin the other, with the outer electrode being copper and the innerelectrode being carbon.

Typically, the inner electrode is a carbon rod and the outer electrodecopper tubing, both of sufficient length, e.g., typically 12 to 36inches to give a suflicient anode area, e.g., 0.5 to 2 square feet.

Electrical connections are connected to the top of the electrodes so asto make the outer electrode (copper) negative and the inside electrode(carbon) positive. If by chance the electrodes are incorrectlyconnected, no harm will be done since the copper electrode will quicklyoxidize forming a copper oxide rectifier thereby stopping furtherpassage of current, i.e., an automatic safety device.

Provision is made toward the bottom of the assembly for the introductionof air between the electrodes. The air serves to circulate the spentsolution upwardly between the electrodes wherein ferrocyanide isconverted to ferricyanide, with the air then serving to cause theregenerated solution to spill over the top of the outer electrode backinto the tank reservoir. Enough air is passed between the electrodes soas to dilute the hydrogen gas given off during the electrolytic stepthereby safeguarding against explosions, as well as sufficient agitationfor promoting gOOd flow of reactants to and from the electrode surfaces.Too much air is to be avoided since it will greatly limit the passage ofcurrent through the cell.

The use of air as opposed to pumps ofiers greater safety, reduced costsand better contact.

The high regeneration capacity (40 to 50 amperes per square foot), aswell as compactness of the assembly (typically it can be a 3 inchdiameter by 24 inches high unit, or less), make it suitable forinstallation in practically any place in the bleach system of thephotographic process. Unlike chemical oxidation systems forregeneration, it can be installed in the circulation system of thebleach, or even in the process equipment. In further contrast with theresidual oxidizing chemicals left in chemical regeneration, the presentsystem allows the ferrocyanide level to be kept very low e.g., less than0.1 gram per liter since the electrolytic regeneration is limited by theamount of ferrocyanide to be oxidized.

The various aspects and modifications of the present invention will bemade more clearly apparent by reference to the following example,drawing and accompanying description.

DRAWING The drawing shOWs the electrolytic system of the presentinvention for regeneration of spent bleach solution.

Turning to the drawing, shown therein is a tank 10 containing the bleachsolution 11 to be regenerated. Because of its compactness, it may beplaced in the bleach circulation system, or bleach circulated thereto bymeans of conduit 17 having valve 14.

Typical bleach solutions known in the art can be treated by the presentinvention. By way of example, a solution having the followingcomposition based on one liter of solution has been found to be quiteeffective in processing all color films currently manufactured in theUnited States and abroad.

Water t. 700 ml. Sodium or potassium ferrocyanide 54 grams. Sodium orpotassium bromide or chloride, or both, total amount 15 grams. Sodiumsulfate (anhydrous), add water to make one liter solution 14 grams-Glacial acetic acid Sufficient to adjust the pH to 4.5 during oxidationof the ferrocyanide to ferricyanide.

pH can be adjusted during regeneration by addition of HCl or HBr acid sothat hydrogen ion as well as halides is supplied to the aboveformulation. In this event, part or all of the alkali bromide orchloride can be eliminated. In all events, the solution contains 15grams/liter of halide, and its pH is adjusted to about 4.5.

In accordance with the present invention, positioned within tank 10 aretwo generally cylindrical electrodes. Outer electrode 16 is typicallycopper and inner electrode 15 is a carbon rod or cylinder.

A typical assembly employs a copper tube three inches in diameter, 24inches long, and a carbon rod two inches in diameter, which is also 24inches long. This gives an anode area. of about one square foot.

The tubes are connected to an electrical power source by connections 18,normally at their top portion, so that the outer copper tube isnegatively charged, and the inner carbon tube positively charged.

Using a D.C. power supply of 3.2 volts, normal operating currents offrom 40 to 50 amperes occur.

Use of a copper tube is necessary to convert nascent hydrogen todiatomic hydrogen due to the formation of Cu H (copper hydride). Nascenthydrogen essentially does not exist due to this rapid conversion on thesurface of the cathode so that ferricyanide formed at the anode is notconverted to ferrocyanide. In contrast, prior art systems employphysically separate solutions by use of diaphragms.

Further, if the copper tube was reversed in charge, i.e. positivelycharged, it becomes a copper oxide rectifier with essentially no flow ofcurrent thereafter.

Air is introduced by one or more inlets 12 and 13 positioned so that theair moves up the annular passage 20 between the electrodes.

The electrodes are immersed in the spent bleach solution 11 in tank sothat the top of the electrodes is a short height, e.g., 4 inches, abovethe level 19 of solution to be regenerated. The air introduced intoannular pas sageway 20 forces the liquid upwardly, forcing it to spillover the top of the outer electrode into the main body of the solution,thereby creating a constantly circulating stream of solution between theelectrodes. The amount of air introduced is controlled carefully forbest agitational circulation, as well as dilution of evolved hydrogen atthe cathode to minimize danger of explosions. Too much air isundesirable since excessive agitation will greatly limit the passage ofcurrent through the cell.

In the example given, air is introduced at a rate of 0.5 ftF/min. intothe annular passage which is one inch in diameter.

While shown in vertical orientation, the electrodes can be inclined solong as sufficient vertical component in the annular passageway existsso that the air is allowed to move upwardly to cause circulation, andspillage of regenerated solution over the top of the electrode into themain solution reservoir.

However, while it might be expected that other possible configurationsdefining an elongated passageway other than cylindrical-shapedelectrodes could be used, it has been found that flat plates or rods donot oifer the advantages of the present system. Difficulty of obtaininguniform agitation, formation of pockets of hydrogen, and sludging withfouling of electrodes were encountered. It was diflicult to use suchflat plate configuration as a means of pumping solution.

Having described the present invention, that which is sought to beprotected is set forth in the following claims.

What is claimed is:

1. In an electrolytic process for regenerating a spent photographicbleach solution containing ferrocyanide to be converted to ferricyanide,the improvement which comprises establishing an annular zone between aninner positively charged electrode and an outer negatively chargedelectrode positioned within a reservoir of spent bleach solution,introducing sufi'icient air upwardly through said annular zone so as tocreate a circulation of spent solu tion undergoing regeneration betweenthe electrodes and to dilute evolved hydrogen so as to safeguard againstexplosion.

2. The improvement of claim 1 which further comprises flowing air so asto circulate spent bleach solution from said reservoir into and up saidannular zone, and then returning regenerated solution over the top ofthe outer electrode back into said solution reservoir.

3. The improvement of claim 1 wherein the ferrocyanide level of thespent bleach solution is less than 0.1 gram per liter.

4. The improvement of claim 1 wherein operating currents of 40 toamperes per square foot are used across said electrodes.

5. The improvement of claim 1 wherein air is introduced upwardly throughthe annular zone at a rate of 0.5 ftfi/min.

References Cited UNITED STATES PATENTS 1,908,516 5/1933 Klempt 423-367 X2,856,353 10/1958 Miller 20486 X 3,104,221 9/1963 Hill 204-272 X OTHERREFERENCES Indian J. Technol., vol. 4, January 1966. Krishna et al., pp.8-11.

MARY F. KELLEY, Primary Examiner US. Cl. X.R.

1. IN AN ELECTROLYTIC PROCESS FOR REGENERATING A SPENT PHOTOGRAPHICBLEACH SOLUTION CONTAINING FERROCYANIDE TO BE CONVERTED TO FERRICYANIDE,THE IMPROVEMENT WHICH COMPRISES ESTABLISHING AN ANNULAR ZONE BETWEEN ANINNER POSITIVELY CHARGED ELECTRODE AND AN OUTER NEGATIVELY CHARGEDELECTRODE POSITIONED WITHIN A RESERVOIR OF SPENT BLEACH SOLUTION,INTRODUCING SUFFICIENT AIR UPWARDLY THROUGH SAID ANNULAR ZONE SO AS TOCREATE A CIRCULATION OF SPENT SOLUTION UNDERGOING REGENERATION BETWEENTHE ELECTRODES AND TO DILUTE EVOLVED HYDROGEN SO AS TO SAFEGUARD AGAINSTEXPLOSION.